This is a Provisional Application Ser. No. 60/012,172 filed Feb. 23, 1996.
This invention relates generally to improvements in prosthetic devices used for reconstruction of the human knee joint. More particularly, this invention relates to an improved tibial prosthesis for a prosthetic knee, including a mobile bearing component adapted to better accommodate a natural range of flex knee motion and force loads applied to the knee joint.
Prosthetic knee joints are generally known in the art and typically comprise matingly configured tibial and femoral prostheses adapted respectively for implantation onto the upper end of a resected tibia and the lower end of a resected femur. The tibial prosthesis incorporates a plastic meniscal bearing member which defines upwardly presented medial and lateral condylar recesses for respective seated engagement of convexly curved medial and lateral condyles on the femoral component. In this regard, the overall geometry of the tibial and femoral prostheses, particularly with respect to the condylar recesses and related femoral condyles, generally resembles the physiology of the natural human knee joint. Desirably, the femoral condyles are retained in seated bearing engagement with the meniscal bearing member throughout a range of natural knee flexion and loading by means of the natural connective tissues including the ligament and tendon structures of the knee joint.
However, the complex mechanical structure of the human knee joint has made it extremely difficult to design an optimum prosthetic joint. More specifically, within a normal range of knee flexion, the natural knee encounters a combination of rolling and sliding motion such that the pivot axis and related contact points between the femur and tibia shift with the degree of knee flexion. This complex motion has made it extremely difficult to design an optimum prosthetic knee capable of emulating natural knee motion while withstanding the relatively high force loads to which the knee joint can be subjected.
One approach for a purportedly improved knee prosthesis involves mounting of the tibial bearing member to permit at least some shifting movement thereof relative to the tibial component which is anchored to patient bone. See, for example, U.S. Pat. No. 5,071,438. This concept involves a pin or post projecting downwardly from the bearing member, at a location beneath the medial condylar recess, for reception into a shallow recess formed in the tibial component. The post and recess are designed to permit a degree of anterior-posterior displacement of the bearing member, relative to the tibial component, to better accommodate natural knee motion with minimum bearing component wear. Unfortunately, however, this concept has suffered from an unacceptable frequency of dislocation and thus has not achieved any widespread acceptance or use.
The present invention pertains to an improved tibial prosthesis of the type having a mobile bearing component, but wherein the mobile bearing component is mounted and constrained in a manner that reduces the likelihood of undesirable dislocation of the prosthesis components.